U.S. Secretary of Defense Chuck Hagel is welcomed by Jordan's Chairman of Defense Lieutenant General Mashal al-Zaben, right, upon his arrival at Marka International Airport in Amman, Jordan, Wednesday, May 14, 2014. Hagel is on a regional tour focusing on Iran's nuclear programm and Syria's civil war. (AP Photo/Mandel Ngan, Pool)
(The Associated Press)

U.S. Secretary of Defense Chuck Hagel is welcomed by Jordan's Chairman of Defense Lieutenant General Mashal al-Zaben, right, upon his arrival at Marka International Airport in Amman on Wednesday, May 14, 2014. Hagel is on a regional tour focusing on Iran's nuclear programm and Syria's civil war. (AP Photo/Mandel Ngan, Pool)
(The Associated Press)

U.S. Secretary of Defense Chuck Hagel, second left, speaks with Jordanian Regent Faisal bin Hussein, center, and Defense Lieutenant General Mashal al-Zaben, second right, during a meeting upon his arrival at Marka International Airport in Amman, Jordan, Wednesday, May 14, 2014. Hagel is on a regional tour focusing on Iran's nuclear program and Syria's civil war. (AP Photo/Mandel Ngan, Pool)
(The Associated Press)

JEDDAH, Saudi Arabia – Defense Secretary Chuck Hagel reassured Persian Gulf allies Wednesday of U.S. commitments to defend them amid tensions in the U.S.-Saudi relationship, including differences over how to help moderate rebel forces remove President Bashar Assad from power in Syria.

Hagel's visit — his third to Saudi Arabia in the past year — was designed to calm Gulf states that feel vulnerable to Iran's influence and are frustrated at U.S. policy on Syria, which has not yet included weapons or other lethal aid in the three-year civil war. Washington also wants to foster more effective, practical forms of defense cooperation on the Arabian Peninsula by integrating their air and missile defense systems.

Hagel addressed the Iran issue at the outset of a meeting of defense ministers from the Gulf states allied with Washington, including Kuwait, Qatar, Bahrain, Oman, Saudi Arabia and the United Arab Emirates.

He made only glancing mention of the Syria problem, which is viewed by the Saudis as a worrying sign of U.S. hesitation to confront Iranian influences in the region. Hagel said Syria reflects a confluence of violent extremism, fragile states and humanitarian emergencies.

"The United States remains committed to working with your governments toward a negotiated, political solution that ends the violence and leads to a representative and responsive government" in Damascus, Hagel said. He made no mention of U.S. military assistance to moderate elements of the forces seeking Assad's ouster.

Secretary of State John Kerry was on his way Wednesday to London for meetings with 10 other foreign ministers to discuss ways to end the crisis in Syria.

The gathering in London and Hagel's meetings come on the heels of key Syrian opposition leader Ahmad al-Jarba's visit last week to Washington. The rebels have renewed their calls for heavy weaponry, such as anti-armor rockets, to combat the deluge of the Syrian government's barrel bombings and other attacks against rebel-held areas.

In remarks to reporters, Hagel said the discussion with his Gulf counterparts about closer coordination of aid to Syrian rebels referred only to non-lethal assistance. He said he did not suggest to Gulf allies that they should provide shoulder-fired anti-aircraft missile to the rebels.

"We pledged to deepen our cooperation in providing aid to the Syrian opposition. We agreed that our assistance must be complementary - and that it must be carefully directed to the moderate opposition," Hagel said.

The Saudis feel more urgency to toppling President Bashir Assad because they see it as an opportunity to blunt the regional influence of Iran, which supports Assad through the Lebanese Shiite militia group Hezbollah.

Anthony Cordesman, an expert on Mideast defense issues at the Center for Strategic and International Studies, said Wednesday in an email exchange that he believes the U.S. Is playing a "very limited role" in providing weapons and training to rebel forces.

"We have a very low profile in the field in Syria," he said, adding that the White House has not supported U.S. military recommendations for stronger cooperation with rebel groups.

Hagel promised the Gulf leaders that "under no circumstances" will the international negotiations with Iran this week in Vienna "trade away regional security for concessions on Iran's nuclear program."

"We will continue to hold Iran accountable for its destabilizing activities across the region," he added. "And we will continue working closely with all of our friends and partners in the Gulf to reinforce their defenses against these destabilizing activities."

Other U.S. officials said during President Barack Obama's visit to Saudi Arabia in March that the administration might be considering allowing shipments to the rebels, possibly from the Saudi government, of shoulder-fired anti-aircraft missiles. Later, State Department spokeswoman Marie Harf denied this was under consideration and said it was not even discussed during Obama's visit.

Up to now the U.S. has limited its assistance to small arms, ammunition and humanitarian assistance out of concern that a wider flow of weaponry could fall into the hands of extremist groups and draw the U.S. deeper into a conflict that is not a vital U.S. interest.

Jarba made his case in Washington this week for greater U.S. assistance. He held talks at the Pentagon and at the White House, which said afterward that Jarba affirmed his commitment to a non-military solution to the crisis. The White House made no mention of whether, as expected, Jarba made a renewed pitch for more U.S. arms.

The main focus of Hagel's visit to Jeddah was the meeting of Gulf defense ministers who consult on military and security policy issues as members of the Gulf Cooperation Council. It was the first time since 2008 that their meeting included an American secretary of defense. Hagel proposed the session when he was in Bahrain last December, saying he believes closer defense coordination is a key to improving security.

Syria and Iran will again be central topic when Hagel briefly visits Amman, Jordan on Wednesday and during two days of meetings in Tel Aviv and Jerusalem later this week.